Leveling instruments employing one or more bubble vials for indicating level in horizontal and vertical planes include a wide range of measuring and layout tools, for example, spirit levels, tapes, laser tools, squares, and the like, and other equipment such as tripods, equipment platforms, and the like. Bubble vials are now mostly made from transparent acrylic material and typically have a symmetrical barrel shaped cavity mostly filled with a typically UV resistant non-freezing vial liquid leaving a small lengthwise directed ellipsoidal bubble floating at the top of its cavity on placing a spirit level on a horizontal surface. The vial liquid has a concave meniscus due to the surface tension of the non-freezing vial liquid. The bubble is an air bubble, a noble gas bubble, or the like. Either a bubble cavity's internal surface or a bubble vial's outside surface is provided with a pair of spaced apart reference markings by means of which a user interprets whether a surface is level or plumb by sighting one or both of its bubble's curved meniscus ends relative to its reference markings. Horizontal bubble vials are typically designed such that their bubbles fit snugly between their spaced apart reference markings on placing same on a horizontal surface. However, craftsmen often have difficulty in accurately determining the precise location of a bubble.
Considerable prior art attempts have been made over the years to assist in the readability of bubble vials for determining accurate bubble location.
U.S. Pat. No. 692,097 to Wood illustrates and describes filling a spirit level with a fluorescent liquid and providing a background for enabling color contrasting of an air bubble to its surrounding vial liquid. The background may be supplied by painting or otherwise coloring the tube itself or by a mirror or by applying a strip of paper bearing the desired color stripe. FIG. 3 is a top plan view showing a strip of paper with a colored stripe suitable for use as background in FIG. 1's top plan view.
U.S. Pat. No. 771,803 to Bishop illustrates and describes a spirit level filled with a practically opaque vial liquid to leave an air bubble and an elongated background member in the form of a rod, stem or spindle, which is of a different color to the vial liquid and is clearly visible through the air bubble.
U.S. Pat. No. 2,362,872 to Weagle illustrates and describes a spirit device filled with a transparent vial liquid to leave an air bubble and having a luminous material on an opposite side from a user. Light passing through the bubble vial and the vial liquid excites the luminous material. The luminous material can be either embedded in a bubble vial container or on the surface thereof. The spirit device may also be provided with opaque guide lines on the luminous material for assisting in accentuating the air bubble's outline.
U.S. Pat. No. 5,414,937 to Denley illustrates and describes a headlamp indicating device with a highlighted bubble vial. The indicating device includes a bubble vial filled with a transparent vial liquid to leave an air bubble. The indicating device includes an underlying scale to indicate the degree of tilt of the bubble vial from horizontal. The indicating device optionally includes a strip of black material adapted to be secured around the bubble vial and a black tinted plastic cap such that the resulting image when viewing the bubble vial from above is a black lined oval positioned over the black lined scale (see Col. 4, lines 19 to 22).
U.S. Pat. No. 6,957,494 to Foran illustrates and describes a bubble vial filled with a transparent vial liquid to leave an air bubble and having a pair of dark colored bands which enhance a bubble's visibility by their reflection on the phase interface between the vial liquid and the air bubble to predominantly dark color a bubble's opposite curved meniscus ends. The bands may be opaque or translucent or tinted such that some light passes through them. The bands may be positioned on the exterior surface of the vial body, an interior surface or between the interior and exterior surfaces. Alternatively, the bands can be integral with vial body and, in such cases, be may be comprised of opaque or translucent portions. The vial may further include end closures which are dark colored and provide further reflection to the phase interface in addition to that of the bands (see Col. 3, lines 1 to 7).
US Patent Application Publication No. 2006/0037204 to Gruetzmacher illustrates and describes a two phase bubble vial including a colored gas bubble. The colors of the vial liquid and the reference markings on the bubble vial's exterior surface can be selected to further enhance the contrast between the gas bubble and the vial liquid and/or the reference markings.
US Patent Application Publication No. 2007/0246116 to Peak et al. illustrates and describes a drainage pipe slope measuring device including a bubble vial for providing a user with a visual indication of the slope of a drainage pipe. FIG. 2 shows a window overlying the bubble vial and having separately colored green and red regions to provide a user with further visual contrast in a top plan view of the bubble vial. The green and red regions can alternatively be formed on the bubble vial's upperside surface as described in para. [0029] 2nd sentence.
US Patent Application Publication No. 2009/0139102 to Kallabis illustrates and describes a spirit level with a bubble vial mounted in a bubble vial housing with opposite colored end face regions for providing a high contrast between the end of an air bubble and its surrounding vial liquid.
PCT International Application No. PCT/IB2003/004391 entitled High Contrast Spirit Level Vial and published under PCT International Publication No. WO 2004/044524 illustrates and describes a two phase bubble vial including a liquid globule floating on a liquid medium. The colors of the liquid globule and the liquid medium are selected for enhanced color contrasting.
Commonly owned PCT International Application No. PCT/IL2006/001475 entitled Bubble Vial having Improved User Readability and published under PCT International Publication No. WO 2007/072489 illustrates and describes several constructions for achieving improved user readability. Such constructions include inter cilia an elongated leveling aid, color contrasting light sources and vial liquids.